Investigation on Multiphase Erosion–Corrosion of Elbow in LPG Desulfurization Unit

Abstract

Severe leakages of the elbow occur in the regeneration tower return pipeline of the LPG desulfurization unit, leading to the unplanned shutdown of the unit frequently over the period of four months. It is forced to apply additional steel plates to prevent the leakage. Elusively, it is found that the first wall contact with the fluid is fully eroded away in the vicinity of the bend, however, the walls of additional steel plates are intact. The clarification of this problem is required to ensure safe production. This strange phenomenon can be investigated by failure analysis and computational fluid dynamics (CFD) simulation. The failure analysis showed that the gas–liquid two-phase erosion–corrosion was the main cause of elbow leakage. The simulation shows that droplet erosion plays a dominant role in the erosion–corrosion process, and the elbow will leak in 4.3 months, which matches the actual situation very well. Furthermore, multiphase erosion–corrosion behavior was thoroughly investigated to expose the feature of the mentioned strange phenomenon. It was shown that when the corrosion holes are formed, the gas forms a fluid vortex in the holes. The vortex acts as flexible substrates, which plays a buffer layer to the droplet erosion, thus protecting the additional steel plate. The formation of the holes provides an effective way for elbow failure prevention.